Here are a few things to check ... ::

"Water Type" setting under the Sonar tab to "Fresh" ...
"Max Depth" setting under Sonar tab to 10' below deepest water in your lake ...
"Noise Filter" setting under Sonar tab to as low as possible without excess clutter showing ...
"Restore Defaults" under Setup tab ...

Check xducer for level with the water surface ...

Rickie